Currently, all dual-pulse LIBS technologies use two laser devices to achieve dual-pulse excitation by means of power supply controlled delay, which increases the cost of the system and needs to focus two paths of lasers respectively, and thus makes it difficult to ensure that the two paths of lasers are focused on the sample to be detected at a same point, and dual-pulse plasma excitation with maximum efficiency cannot be achieved.
Laser Induced Breakdown Spectroscopy (LIBS) is a quantitative analytical technique of emission spectrums generated based on interaction between lasers and materials. This method needs only several micrograms in the measurement process, and therefore can implement non-destructive measurement; element analysis on substances in any physical state can be realized without sample pretreatment, so that the LIBS technology is widely used. The LIBS technology is an optical technology application that can measure and analyze samples as far as tens of meters away, and Its remote analysis capability is very attractive in dangerous, high-temperature or hostile environments. LIBS technology for component analysis lasts only about ten seconds in the entire process, and has good real-time and rapidness. The LIBS technology can be used to quantitatively analyze trace substances by means of calibration, and the limit of detection and accuracy completely satisfy application requirements.
Compared with conventional detection technologies, LIBS technology has unparalleled technical advantages for online in situ detection. However, as a single-pulse LIBS technology has low analytical sensitivity, the application in the trace element detection field is limited. LIBS generates transient plasmas based on interaction between high-power lasers and substances to research emission spectrums of plasmas, so as to achieve qualitative analysis and quantitative analysis on sample components. However, the plasma temperature and density of the single-pulse LIBS excitation are low, and the intensity of the emitted emission spectrum is limited, so the analytical sensitivity is relatively low.
The dual-pulse LIBS technology is to generate plasmas by irradiating a surface of a sample by using a first beam of laser pulse, and subsequently, irradiate the plasmas by using a second beam of laser pulse to enhance spectral line emission, so as to implement two phase distribution optimization of material ablation and plasma excitation and therefore the dual-pulse LIBS technology can effectively improve the signal to noise ratio and the analytical sensitivity. Currently, all the dual-pulse LIBS technologies use two nanosecond lasers to achieve dual-pulse excitation by means of power supply controlled delay, which increases the cost of the system and needs to focus two paths of lasers respectively, and thus makes it difficult to ensure that the two paths of lasers are focused on the sample to be detected at a same point, and dual-pulse plasma excitation with maximum efficiency cannot be achieved.
By exploring results of detection on steel samples by using ultrashort pulse lasers with different pulse widths and analysis of the dual-pulse LIBS technology, we find that two pulse lasers can be generated by using single pulse laser device, wherein the first pulse laser is a nanosecond laser, and the second pulse laser is a picosecond laser; and the two pulse lasers are focused on the sample to be detected at a same position; a surface of the sample is irradiated by using a first beam of nanosecond laser pulse to generate plasmas; and subsequently, the plasmas are irradiated by using a second beam of picosecond laser pulse to enhance spectral line emission, so as to achieve two phases distribution optimization of material ablation and plasma excitation, and therefore the signal to noise ratio can be effectively improved and the analytical sensitivity is promoted. We have developed a dual-pulse laser induced plasma spectral analysis device, with laser pulse widths including two specifications: picosecond and nanosecond.